1. Field of the Invention
The present invention relates to a thermal transfer film and particularly to a thermal transfer film which can yield a thermally transferred print possessing excellent fastness or resistance properties such as excellent abrasion resistance, lightfastness, and alteration preventive property, is less likely to cause damage to an object, is free from a deterioration in quality of the print, and does not incur an increase in production cost, a process for producing the thermal transfer film, a method for image formation using the thermal transfer film, and an image formed object.
2. Prior Art
Thermal transfer can easily record variable information and thus is extensively used in a wide variety of applications. The thermal transfer is a method which comprises the steps of: putting a thermal transfer film, comprising a colorant layer provided on a substrate, on top of an object optionally provided with a receptive layer; pressing the assembly between a heating device, such as a thermal head, and a platen roll; and selectively heating the heating device in its heating portion according to image information to transfer the colorant contained in the colorant layer on the thermal transfer film onto the object, whereby an image is recorded on the object. Thermal transfer methods are roughly classified into thermal ink transfer (hot melt-type thermal transfer) and thermal dye sublimation transfer (sublimation-type thermal transfer).
The thermal ink transfer is a method for image formation wherein a thermal transfer film bearing thereon a heat-fusion ink layer is heated by the above heating means and the component of the softened heat-fusion ink layer is transferred onto an object such as natural fiber paper or plastic sheet to form an image. The heat-fusion ink layer used herein is formed of a dispersion of a colorant, such as a pigment, in a binder, such as heat-fusion wax or resin and is supported on a substrate such as a plastic film. The formed image has high density and high sharpness, and this method is suitable for recording binary images such as characters and line drawings.
On the other hand, the thermal dye sublimation transfer is a method for image formation wherein a thermal transfer film bearing thereon a sublimable dye layer is heated by the above heating means to sublimate and transfer the sublimable dye contained in the dye layer onto a receptive layer provided on an object, whereby an image is formed on the object. The sublimable dye layer used herein is formed of a solution or dispersion of a sublimable dye used as the colorant in a binder resin and is supported on a substrate film such as a plastic film. According to this method, since the amount of the dye transferred can be regulated dot by dot according to the quantity of energy applied to a heating device, such as a thermal head, the reproduction of gradation can be realized by varying the density.
Thus, the thermal ink transfer method and the thermal dye sublimation transfer method have respective features, that is, the thermal ink transfer method can easily and clearly form images of characters, numerals and the like, while the thermal dye sublimation transfer method is excellent in gradation rendering and can form images such as a photograph-like image of a face in a faithful, clear manner.
Images formed by the above thermal transfer methods, independently of whether the images have been formed by the thermal ink transfer method or the thermal dye sublimation transfer method, are unsatisfactory in fastness or resistance properties such as abrasion resistance, lightfastness, and alteration preventive property. To cope with the unsatisfactory fastness or resistance properties, a protective layer has hitherto been formed on the image. For example, Japanese Patent Laid-Open No. 159795/1991 describes that information such as images and letters are formed on a card substrate and a transparent protective layer is provided on at least a part of the surface of the information. In this case, two or more protective layers are transferred so that they overlap with each other and are different from each other in transfer area. At least one of the protective layers contains a brightening agent and/or an ultraviolet absorber. In this method, however, since the transfer of the protective layer is carried out twice or more, damage to the object is large. Further, the number of steps (transfer) necessary for preparing a print is large, and a great deal of time is required. Therefore, for example, a deterioration in print quality and an increase in production cost are disadvantageously likely to occur.
Japanese Patent Laid-Open No. 177249/2000 describes a record produced by forming a color image on recording paper and forming a transparent image of a transparent ink on the color image and further discloses that an overcoat is formed between the color image and the transparent image. The claimed advantage of the record is to improve the weathering resistance and abrasion resistance of the color image and to permit the transparent image on the color image to be viewed by the reflection of light according to the angle of the line of sight to the transparent image recorded face. Also in this case, however, since the transfer onto the color image on the recording paper is carried out a plurality of times, that is, since the transparent image and the overcoat are transferred onto the color image on the recording paper, damage to the object is large. Further, the number of steps (transfer) necessary for preparing a print is large, and a great deal of time is required. Therefore, for example, a deterioration in print quality and an increase in production cost are disadvantageously likely to occur.
The present invention has been made with a view to solving the above problems of the prior art, and it is an object of the present invention to provide a thermal transfer film which can yield a thermally transferred print possessing excellent fastness or resistance properties such as excellent abrasion resistance, lightfastness, and alteration preventive property, is less likely to cause damage to an object, is free from a deterioration in quality of the print, and does not incur an increase in production cost, a method for image formation using the thermal transfer film, and an image formed object.
The above object can be attained by a thermal transfer film comprising: a substrate; and one or a plurality of layers including a thermal transfer layer provided on one side of the substrate, the thermal transfer layer being located on the uppermost surface of the thermal transfer film, a convex being provided on a part of the thermal transfer layer.
According to a preferred embodiment of the present invention, the thermal transfer layer comprises mainly of a thermoplastic resin having a glass transition temperature of 50 to 120xc2x0 C. The use of this resin can provide good transferability and fixation onto an object.
More preferably, the thermoplastic resin is selected from a polyester resin having a number average molecular weight of 2000 to 30000, a vinyl chloride-vinyl acetate copolymer having an average degree of polymerization of 150 to 500, and a homopolymer or copolymer, of a methacrylate base monomer, having a weight average molecular weight of 20000 to 60000. The use of this resin can improve the function of the thermal transfer layer, after transfer onto the object, as the protective layer, that is, can improve fastness or resistance properties such as abrasion resistance, lightfastness, and alteration preventive property.
In another embodiment of the thermal transfer film according to the present invention, a release layer is provided between the substrate and the thermal transfer layer, and the release layer is not separable from the substrate side. The provision of the release layer can improve the transferability of the thermal transfer layer.
Preferably, a peel layer is provided between the substrate and the thermal transfer layer, and the peel layer is separable from the substrate side. The provision of the peel layer can improve transferability because, in transfer onto an object, the thermal transfer layer, together with the peel layer, is transferred from the thermal transfer film.
More preferably, the peel layer is provided between the release layer and the thermal transfer layer. This facilitates the transfer of the thermal transfer layer together with the peel layer onto an object.
In the thermal transfer film according to the present invention, preferably, the convex provided in the thermal transfer layer has a height of 0.2 to 5.0 xcexcm. When the height of the convex is in the above-defined range, the convex in the thermal transfer layer transferred onto the object becomes easily legible by the reflection of light according to the angle of the line of sight to the transfer face.
According to another aspect of the present invention, there is provided a process for producing a thermal transfer film, said process comprising the steps of: providing two thermal transfer films each comprising a substrate and one or a plurality of layers including a thermal transfer layer provided on the substrate, the thermal transfer layer being located on the uppermost surface of the thermal transfer film; putting the two thermal transfer films on top of each other so that the thermal transfer layer in one of the thermal transfer films faces the thermal transfer layer in the other thermal transfer film; and partially heating the assembly of the thermal transfer films to transfer a part of the thermal transfer layer in one of the thermal transfer films onto the thermal transfer layer in the other thermal transfer film, whereby a convex is formed on a part of the thermal transfer layer in one of the thermal transfer films. The thermal transfer layer in the thermal transfer film comprising a thermal transfer layer having a convex in a part thereof provided on one side of the substrate at a position most remote from the substrate is transferred onto an object. For example, an image is previously provided by the thermal transfer recording or the like on the object onto which the thermal transfer layer is transferred, and the thermal transfer layer is transferred onto the image. This can protect the image and permits the convex in the thermal transfer layer transferred onto the object to be legible by the reflection of light according to the angle of the line of sight to the image recorded face.
According to still another aspect of the present invention, there is provided a method for image formation using the thermal transfer film according to the present invention, said method comprising the steps of: putting the thermal transfer film on top of a thermal transfer recording medium comprising a substrate and, provided on at least one side of the substrate, a thermal transfer ink layer comprising a thermoplastic resin and a colorant so that the thermal transfer layer faces the thermal transfer ink layer; imagewise heating the stacked thermal transfer recording medium to imagewise transfer the thermal transfer ink layer or the colorant onto the thermal transfer layer in the thermal transfer film, whereby a reverse image is once formed on the thermal transfer film; then putting the thermal transfer film with the reverse image formed thereon on top of an object so that the thermal transfer layer in the thermal transfer film faces an image forming face in the object; and heating the stacked thermal transfer film from the surface thereof remote from the thermal transfer layer to transfer the thermal transfer layer with the reverse image formed thereon onto the object, whereby an image is formed on the object.
Further, the thermal transfer layer is preferably transparent or translucent. According to this construction, even when the convex in the thermal transfer layer overlaps with the image of the thermal transfer ink layer, the image can be clearly viewed because the convex and the image do not affect each other.
More preferably, the light transmission properties of the convex in the thermal transfer layer are different from those of the portion other than the convex in the thermal transfer layer. This can render the convex in the thermal transfer layer conspicuous.
According to a further aspect of the present invention, there is provided an image formed object (a thermal transfer print) comprising an image formed on an object by the above method for image formation. In the image formed object produced by this method, the image formed by the transfer of the thermal transfer ink layer is protected by a transparent or translucent thermal transfer layer and thus possesses excellent fastness or resistance properties such as abrasion resistance, lightfastness, and alteration preventive property. Further, the convex in the thermal transfer layer transferred onto the object is legible by the reflection of light according to the angle of the line of sight to the image recorded face of the image formed object.
Further, the thermal transfer film, wherein the thermal transfer layer having a convex in a part thereof is provided on one side of the substrate at its position most remote from the substrate and an image has been formed by the transfer of the thermal transfer ink layer from the thermal transfer recording medium provided with the thermal transfer ink layer, can function as an intermediate transfer recording medium, and a thermal transfer layer as a protective layer and a convex can be formed on the object by a single transfer operation. Therefore, this can reduce damage to the object caused by the transfer and can suppress a deterioration in image quality and an increase in production cost.